Surgical heart valve replacement has been performed in human beings for many years. Most frequently, the procedures are utilized to replace mitral or aortic valves in patients who suffer from valvular heart disease.
The four valves separate each ventricle from its associated atrium, or from the ascending aorta (left ventricle) or pulmonary artery (right ventricle). After the valve excision, the annulus generally comprises a ledge extending into and defining the orifice between the respective chambers. Prosthetic valves may attach on the upstream or downstream sides of the annulus ledge, but outside of the ventricles to avoid interfering with the large contractions therein. Thus, for example, in the left ventricle a prosthetic valve is positioned on the inflow side of the mitral annulus (in the left atrium), or on the outflow side of the aortic annulus (in the ascending aorta).
The annuluses comprise dense fibrous rings attached either directly or indirectly to the atrial and ventricular muscle fibers. In a valve replacement operation, the damaged leaflets are excised and the annulus sculpted to receive a replacement valve. Ideally the annulus presents relatively healthy tissue that can be formed by the surgeon into a uniform ledge projecting into the orifice left by the removed valve. The time and spacial constraints imposed by surgery, however, often dictate that the shape of the resulting annulus is less than perfect for attachment of a sewing ring. Moreover, the annulus may be calcified as well as the leaflets and complete annular debridement, or removal of the hardened tissue, results in a larger orifice and less defined annulus ledge to which to attach the sewing ring. In short, the contours of the resulting annulus vary widely after the natural valve has been excised, and sizing is often problematic.
In general, prosthetic aortic valves comprise a cylindrical valve body having a blood flow passageway extending longitudinally therethrough, and a suture ring formed annularly thereabout. The suture ring comprises suture penetrable material or a series of suture passage apertures, to facilitate anastomosis of the suture ring to the adjacent surgically-prepared aortic annulus. Because of the tricuspid configuration of the endogenous aortic valve, the natural aortic root has a non-planar, multi-curvate configuration. To correspond to such anatomical configuration of the natural aortic root, some or all of the aortic prosthetic valves of the prior art have utilized suture rings that are of a generally non-planar, multi-curvate configuration.
Conventional placement of the valve is intra-annular, with the valve body deep within the narrowest portion of the annulus to enhance any seal effected by the sewing ring/suture combination and reduce the chance of perivalvular leakage. To enable placement of the valve deep within the annulus, the sewing ring is compressed against the rigid valve body to match the annulus diameter. However, placement of the valve within the natural orifice naturally reduces the resulting flow orifice because of the thickness of the prosthetic valve. Therefore, some surgeons prefer, or some patients indicate, a supra-annular placement. In this position, only the rigid mounting portion of the valve enters the annulus, with the compressible sewing ring seated above the annulus, thus permitting a larger valve (larger flow orifice) to be implanted.
The ultimate success of any valve placement procedure is dependent on a number of factors, including the correct sizing and placement of the prosthetic valve. In this regard, it is common practice to utilize a sizing obturator to determine the correct size of prosthetic valve for implantation. Such sizing obturators typically comprise a series of different-sized cylindrical members (sometimes color-coded for size identification) that are independently attachable to a handle, and which are insertable into the surgically-prepared valve annulus to determine the actual size of the annular opening. Sizing obturators of the prior art typically comprise a generally cylindrical obturator body having a flat annular flange extending therearound. The flat annular flange is typically advanced into abutment with, but does not actually seat or nest within, the non-planar, three-peaked anatomy of the natural aortic root, which defines the superior aspect of the aortic annulus.
Examples of aortic and mitral valve sizing obturators of the prior art include the True-Size™ Aortic Obturator-Model 1161 and the True-Size™ Mitral Obturator-Model 1162, Baxter Healthcare Corporation, CVS Heart Valve Therapy Division, 17221 Red Hill Ave., Irvine, Calif. 92614. When the appropriate sizer is found, the correspondingly sized valve is chosen for implantation. Valves are typically provided in a range of sizes denoting the external mounting diameter in millimeters. Valves are most commonly available in odd 2 mm increments between 21 and 31 mm in diameter.
Over the years, the art of sizing a patient's aortic and mitral tissue annulus in order to select the correct prosthetic valve size has been less than satisfactory, particularly in the aortic position. A number of surgeons have experienced the problem of using a manufacturer's sizer to determine the correct valve size only to find the selected valve is either too large or too small for the patient's annulus. This problem particularly applies to 19, 21 and 23 mm aortic valves. It is also related to the fact that surgeons need to be able to implant the smaller aortic valves in the supra annular or intra annular position.
In spite of ongoing advances in sizing techniques, there exists a need for a more accurate sizing regimen.